Windows sometimes has a mind of its own when it comes to DNS. To clear the windows DNS cache when you have issues do the following. Open cmd or powershell as administrator. Run ipconfig /flushdns

To reset (flush) the DNS cache on Mac OSX depends on the OS version. One of the following commands in the terminal should do it for you. sudo dscacheutil -flushcache or sudo killall -HUP mDNSResponder or sudo discoveryutil mdnsflushcache

The simplest way to reset the DNS cache on your iphone is to switch it to Airplane mode and back. Airplane mode switches of all network connectivity, this has the side effect of clearing the DNS cache.